Quand l’art prend soin de vous

En hommage à Jean-Louis Déotte, Diane Watteau rappelle la fécondité de ses réflexions sur l’art et le care, notamment dans l’analyse par le philosophe d’une exposition organisée à la Pharmacie, un espace pour l’art contemporain situé dans le pavillon Dormois de l’hôpital de Tonnerre à l’été 2017. L’éditorial du no 6 de la revue Plastik lui avait été dédié. Il rendait hommage à son œuvre grâce à des textes qui témoignent de l’impact de sa pensée sur la philosophie, mais également dans les arts plastiques d’aujourd’hui. Les analyses principales de cette lecture sont ici reprises

Soil Microstructures Examined Through Transmission Electron Microscopy Reveal Soil-Microorganisms Interactions

Research over the last few decades has shown that the characterization of microaggregates at the micrometer scale using Transmission Electron Microscopy (TEM) provides useful information on the influence of microorganisms on soil functioning. By taking soil heterogeneity into account, TEM provides qualitative information about the state of bacteria and fungi (e.g., intact state of living organisms, spores, residues) at the sampling date within organo-mineral associations, from the soil-root interface to the bulk soil, and in biogenic structures such as casts. The degree of degradation of organic matter can be related to the visualized enzymatic potential of microorganisms that degrade them, thus indicating organic matter dynamics within soil aggregates. In addition, analytical TEM characterization of microaggregates by EELS (Electron Energy Loss Spectroscopy) or EDX (Energy Dispersive X-rays spectroscopy) provides in situ identification of microbial involvement in the biogeochemical cycles of elements. Furthermore, micrometer characterization associated with other methodologies such as Nanoscale Secondary Ion Mass Spectrometry (NanoSIMS) or soil fractionation, enables monitoring both incorporation of biodegraded litter within soil aggregates and impacts of microbial dynamics on soil aggregation, particularly due to production of extracellular polymeric substances. The present focused review suggests that such an approach using micrometer characterization of soil microhabitats provides relevant qualitative and quantitative information when monitoring and modeling microbial processes in dynamics of organo-mineral associations

Uso da micropedologia na descrição de processos pedogenéticos em Tecnossolos

International audienceTechnosols are characterized by the presence of mineral and organic parent materials of technogenic origin (e.g. agricultural or urban wastes, industrial by-products, building materials, transported natural materials). In view of the continual increase of such man-made soils, there is a true need of understanding their functioning and evolution. Micropedology, i.e. morphological and analytical characterization of pedofeatures on soil sections, appears as a relevant approach to take into account the diversity and the specificity of Technosols in the knowledge of their pedogenetic processes. Micropedology was investigated at microscopic and submicroscopic scale on four Technosols. Therefore, it determined specific features of anthropogenic constituents allowing in situ monitoring until the early stages of Technosol pedogenesis. Organic matter dynamics, soil porosity evolution, impact of faunal activity or hydric conditions on Technosol structure were investigated. Moreover, as Technosol components and deposition modes are diverse, one can expect numerous interfaces. In that way, micropedology appeared particularly well adapted to study these local interfaces as sites of favoured pedogenesis. Supplemented with overall physico-chemical soil analyses, characterization of Technosol pedogenic features using micropedology improves the understanding of their functioning and evolution. In addition, according to the environmental context, such data also give useful information for the Technosol management.RESUMEN Los Tecnosoles se caracterizan por la presencia de materiales orgánicos y minerales de origen tecnogenético (p.ej. residuos agrícolas o urbanos, subproductos industriales, materiales de construcción, materiales naturales transportados, etc.). Dado el aumento continuo de estos tipos de suelos antrópicos, es necesario comprender su funcionamiento y evolución. La micropedología, definida como la caracterización morfológica y analítica de microestructuras de láminas de suelo, es una herramienta estándar para el estudio de los mismos. La micropedología ofrece un enfoque relevante para el conocimiento de los procesos edafogenéticos de los Tecnosoles, ya que permite considerar la diversidad y la especificidad de los mismos. Cuatro tipos de Tecnosoles fueron investigados mediante técnicas de micropedología a escala fotónica y de ultraestructura. Así, fue posible determinar las características de los constituyentes antropogénicos y realizar un seguimiento in situ hasta las fases tempranas de la edafogénesis de estos Tecnosoles. Se investigaron procesos como la dinámica de la materia orgánica, la evolución de la porosidad y el impacto de la actividad de la fauna o de las condiciones hídricas en la estructura de los Tecnosoles. Además, ya que los Tecnosoles son muy diversos tanto en sus componentes como en el modo en que estos componentes se organizan, es esperable que existan numerosas interfaces entre horizontes de suelo. De este modo, la micropedología se adapta muy bien al estudio de estas interfaces locales donde se dan procesos edafogenéticos. La caracterización micropedológica de las microestructuras de los Tecnosoles, complementada con análisis físico-químicos generales, incrementa de modo sustancial la comprensió

Microplastic Detection in Soil Amended With Municipal Solid Waste Composts as Revealed by Transmission Electronic Microscopy and Pyrolysis/GC/MS

Urban compost application in agroecosystems enhances soil fertility but can also be a source of (micro) plastics, which are not completely removed during the composting process. Knowledge of the fate of these plastics in regularly-amended soils is thus an issue for the environmental management of these soils. The aims of this study were (1) to develop a method combining soil fractionation, microscopic observation and chemical characterization to follow the fate of plastics in soils and (2) to apply this method on a long-term experimental field, where municipal solid waste composts were applied every other year during 10 years. The presence of plastics was investigated within compost and soil fractions using morphological and analytical characterization by transmission electronic microscopy (TEM-EDX) and pyrolysis coupled to gas chromatography and mass spectrometry (Py/GC/MS). Specific features of plastics allowed us to distinguish these polymers from soil organic matter even in the <200 μm soil fractions. Ti and Ba detection associated with these features, as they are initially added during the polymer production, also constituted plastic tracers within organo-mineral fractions. Plastic fragments as detected by TEM were less abundant in the fine soil fractions compared to the coarsest ones. The abundance of styrene produced upon pyrolysis, used as a molecular tracer of plastics, also decreased relative to produced toluene according to the same particle size gradient. Our results evidenced that plastics and microplastics were present in the soil that was amended for 10 years with compost, while not in the control soil. MPs were mostly observed as individualized particles, present in the coarsest fractions as well as some of the fine soil fractions, but they were little associated with the soil matrix. They mostly did not show any degradation features such as microbial lysis. We thus suggest that their evolution in soil was mainly due to fragmentation. Our methodological approach provides tools to monitor the fate of microplastics over time and specify the contribution of such contaminants in soil amended with bio-based products

Mechanisms of goethite dissolution in the presence of desferrioxamine B and Suwannee River fulvic acid at pH 6.5

Siderophores are Fe3+ specific low MW chelating ligands secreted by microorganisms in response to Fe stress. Low MW organic acids such as oxalate have been shown to enhance siderophore mediated dissolution of Fe3+ oxides. However, the effect of fulvic acid presence on siderophore function remains unknown. We used batch dissolution experiments to investigate Fe release from goethite in the goethite-fulvic acid desferrioxamine B (goethite-SRFA-DFOB) ternary system. Experiments were conducted at pH 6.5 while varying reagent addition sequence. FTIR and UV-Vis spectroscopy were employed to characterise the Fe-DFOB, Fe-SRFA and DFOB–SRFA complexes. Iron released from goethite in the presence of SRFA alone was below detection limit. In the presence of both SRFA and DFOB, dissolved Fe increased with reaction time, presence of the DFOB-SRFA complex, and where SRFA was introduced prior to DFOB. FTIR data show that in the ternary system, Fe3+ is complexed primarily to oxygen of the DFOB hydroxamate group, whilst the carboxylate C=O of SRFA forms an electrostatic association with the terminal NH3+ of DFOB. We propose that SRFA sorbed to goethite lowers the net positive charge of the oxide surface, thus facilitating adsorption of cationic DFOB and subsequent Fe3+ chelation and release. Furthermore, the sorbed SRFA weakens Fe-O bonds at the goethite surface, increasing the population of kinetically labile Fe. This work demonstrates the positive, though indirect role of SRFA in increasing the bioavailability of Fe3+

Earthworm Cast Formation and Development: A Shift From Plant Litter to Mineral Associated Organic Matter

Earthworms play a major role in litter decomposition, in processing soil organic matter and driving soil structure formation. Earthworm casts represent hot spots for carbon turnover and formation of biogeochemical interfaces in soils. Due to the complex microscale architecture of casts, understanding the mechanisms of cast formation and development at a process relevant scale, i.e., within microaggregates and at the interface between plant residues, microorganisms and mineral particles, remains challenging. We used stable isotope enrichment to trace the fate of shoot and root litter in intact earthworm cast samples. Surface casts produced by epi-anecic earthworms (Lumbricus terrestris) were collected after 8 and 54 weeks of soil incubation in mesocosms, in the presence of 13C-labeled Ryegrass shoot or root litter deposited onto the soil surface. To study the alteration in the chemical composition from initial litter to particulate organic matter (POM) and mineral-associated organic matter (MOM) in cast samples, we used solid-state 13C Nuclear Magnetic Resonance spectroscopy (13C-CPMAS-NMR) and isotopic ratio mass spectrometry (EA-IRMS). We used spectromicroscopic approach to identify plant tissues and microorganisms involved in plant decomposition within casts. A combination of transmission electron microscopy (TEM) and nano-scale secondary ion mass spectrometry (NanoSIMS) was used to obtain the distribution of organic carbon and δ13C within intact cast sample structures. We clearly demonstrate a different fate of shoot- and root-derived organic carbon in earthworm casts, with a higher abundance of less degraded root residues recovered as particulate organic matter on the short-term (8 weeks) (73 mg·g−1 in Cast-Root vs. 44 mg·g−1 in Cast-Shoot). At the early stages of litter decomposition, the chemical composition of the initial litter was the main factor controlling the composition and distribution of soil organic matter within casts. At later stages, we can demonstrate a clear reduction of structural and chemical differences in root and shoot-derived organic products. After 1 year, MOM clearly dominated the casts (more than 85% of the total OC in the MOM fraction). We were able to highlight the shift from a system dominated by free plant residues to a system dominated by MOM during cast formation and development

Effect of desferrioxamine B and Suwannee River fulvic acid on Fe(III) release and Cr(III) desorption from goethite

Siderophores are biogenic chelating ligands that facilitate the solubilization of Fe(III) and form stable complexes with a range of contaminant metals and therefore may significantly affect their biogeochemical cycling. Desferrioxamine B (DFOB) is a trihydroxamate siderophore that acts synergistically with fulvic acid and low molecular weight organic ligands to release Fe from Fe(III) oxides. We report the results of batch dissolution experiments in which we determine the rates of Cr(III) desorption and Fe(III) release from Cr(III)-treated synthetic goethite as influenced by DFOB, by fulvic acid, and by the two compounds in combination. We observed that adsorbed Cr(III) at 3% surface coverage significantly reduced Fe(III) release from goethite for all combinations of DFOB and fulvic acid. When DFOB (270 µM) was the only ligand present, dissolved Fe(III) and Cr(III) increased approximately 1000-fold and 16-fold, respectively, as compared to the ligand-free system, a difference we attribute to the slow rate of water exchange of Cr(III). Suwannee River fuvic acid (SRFA) acts synergistically with DFOB by (i) reducing the goethite surface charge leading to increased HDFOB+ surface excess and by (ii) forming aqueous Fe(III)-SRFA species whose Fe(III) is subsequently removed by DFOB to yield aqueous Fe(III)-DFOB complexes. These observations shed new light on the synergistic relationship between DFOB and fulvic acid and reveal the mechanisms of Fe(III) acquisition available to plants and micro-organisms in Cr(III) contaminated environments

A 300-year record of sedimentation in a small tilled catena in Hungary based on δ13C, δ15N, and C/N distribution

Purpose Soil erosion is one of the most serious hazards that endanger sustainable food production. Moreover, it has marked effects on soil organic carbon (SOC) with direct links to global warming. At the same time, soil organic matter (SOM) changes in composition and space could influence these processes. The aim of this study was to predict soil erosion and sedimentation volume and dynamics on a typical hilly cropland area of Hungary due to forest clearance in the early eighteenth century. Materials and methods Horizontal soil samples were taken along two parallel intensively cultivated complex convex-concave slopes from the eroded upper parts at mid-slope positions and from sedimentation in toe-slopes. Samples were measured for SOC, total nitrogen (TN) content, and SOMcompounds (δ13C, δ15N, and photometric indexes). They were compared to the horizons of an in situ non-eroded profile under continuous forest. On the depositional profile cores, soil depth prior to sedimentation was calculated by the determination of sediment thickness. Results and discussion Peaks of SOC in the sedimentation profiles indicated thicker initial profiles, while peaks in C/N ratio and δ13C distribution showed the original surface to be ~ 20 cm lower. Peaks of SOC were presumed to be the results of deposition of SOC-enriched soil from the upper slope transported by selective erosion of finer particles (silts and clays). Therefore, changes in δ13C values due to tillage and delivery would fingerprint the original surface much better under the sedimentation scenario than SOC content. Distribution of δ13C also suggests that the main sedimentation phase occurred immediately after forest clearance and before the start of intense cultivation with maize. Conclusions This highlights the role of relief in sheet erosion intensity compared to intensive cultivation. Patterns of δ13C indicate the original soil surface, even in profiles deposited as sediment centuries ago. The δ13C and C/N decrease in buried in situ profiles had the same tendency as recent forest soil, indicating constant SOM quality distribution after burial. Accordingly, microbiological activity, root uptake, and metabolism have not been effective enough to modify initial soil properties